This invention relates to the separation of components from a gas mixture. Aspects of the invention relate to the separation of components, for example carbon dioxide (CO2) and/or hydrogen sulphide (H2S) from, for example, acid gas, for example natural gas, syngas or process gas although features of the invention may be applied to other source gases. Such a process is sometimes referred to as acid gas removal (AGR). In examples described herein, the source gas mixture contains CO2 and/or H2S in addition to other components and in some examples, the CO2 and/or H2S components of the gas are referred to as acid gas components. In examples of the invention, some or all of the acid gas component is removed using a solvent absorption method; some examples described use a chemical absorption system (for example including N-Methyl diethanolamine (MDEA)), and others use a physical solvent (for example based on methanol (MeOH)).
Physical absorption, chemical absorption and cryogenic AGR processes transform acid gas component into liquid form by absorption of the acid gas component, for example CO2, by an absorbent. This process is exothermic. Conversely, the process for regeneration of the absorbent transforms the liquid phase acid gas component into gaseous form and this process is endothermic.
Conventional absorption AGR requires an external heat source and/or cooling for operation. For example in a typical chemical absorption AGR system based on MDEA, acid gas component, for example CO2, is absorbed by MDEA solution in an absorption column. A considerable amount of external steam and cooling water is then required for the stripping process to remove the acid gases from the MDEA.
Physical solvent systems include the conventional Rectisol (RTM) process which is based on the use of a methanol (MeOH) as solvent. In the conventional Rectisol process, refrigerated MeOH is used as a solvent for physical absorption of the acid gas components. The acid gas components are absorbed by the MeOH in a low temperature absorption column at a relatively high pressure. The acid gas components are then subsequently desorbed from the solvent by reducing the pressure of the solvent, stripping and, if necessary, reboiling the solvent. A system for heating and cooling various sections of the process is required for its operation. For example, inlet gas is cooled down through a heat exchanger upstream of the methanol solvent, and gas exiting the process is used as a coolant. External refrigeration, for example using propane or ammonia, is required to maintain the column at a low temperature by absorbing the heat generated in the column. External steam and cooling water is also required for the stripper for removal of absorbed components from the MeOH.
The external heating and/or cooling in the conventional processes necessitate a significant energy input in to the system. It would be beneficial to reduce the energy consumption of the absorption AGR processes compared with conventional processes.